INTRODUCTION 

TO 

SUGAR  ANALYSIS. 

* 


NOTES  ON 

Lectures  and  Laboratory  Manipulation. 


BY 

GEO.  Wm.  Rolfe, 

Instructor  in  Sugar  Analysis, 
Massachusetts  Institute  of  Technology. 


BOSTON : 

Printed  for  the  Author. 


These  Notes  in  Their  Present  Unfinished  Form  are 
Printed  Solely  for  the  Convenience  of  Students  of 
The  Massachusetts  Institute  of  Technology,  and  are 
not  Intended  for  General  Publication. 


Copyrighted,  1898, 
By  GEO.  WM.  ROLFE. 


54- 

T64-U 


CONTENTS. 


I.  Synoptic  Lecture  Notes. 

Earlier  Methods  of  Sugar  Analysis  ....  5 

General  Principles  of  Optical  Analysis  ...  5 

Application  to  Sugar  Analysis  ....  7 

Polariscopes  .......  . 7 

Evolution  of  the  Saccharimeter  ....  8 

Saccharimeter  Scales g 

Quartz- Wedge  Saccharimeters  ....  8 

Sources  of  Error  in  Polarizations  ....  9 

Other  Common  Determinations  of  Sugar  Analysis  : 

Moisture  ........  9 

Ash 

Reducing  Sugars  . . . . . .10 

Application  of  Polariscope  Determinations  in  the 
Estimation  of  other  Saccharine  Substances : 

Honey 10 

Laevulose 

Lactose  . . . . . . . .10 

Commercial  Glucose 10 

Worts 

II.  Laboratory  Manipulation . 

General  Notes  and  Directions  Applying  to  Sacchari- 
meters and  Polariscopes  . . . .12 

Care  of  Eyesight  . . . . . .12 

Care  of  Instrument 

Polariscope  Tubes 

Scale  Readings 

Notes  on  Special  Instruments  . . . . .15 

Schmidt  & Haensch  Saccharimeter  . . .15 

Laurent  Polariscope  . . . . . .15 


82568  I 


4 


Soleil-Duboscq  Saccharimeter  .... 

Soleil-Ventzke-Scheibler  Saccharimeter 
Table  of  Special  Laboratory  Exercises 
Quartz-Plate  Comparisons  . 

Scale-Comparisons  with  Glucose  Solutions 
Calibration  of  Flasks  ...... 

Polarization  of  Cane-Sugar  Samples 

Double  Polarization  ...... 

Fundamental  Principles  . 

Clerget’s  Method 

Determination  of  Specific-Rotatory  Powers 
Absolute  Optical  Constants  . 

Birotation  ....... 

Specific-Rotatory  Power  of  Commercial  Glucose 
Brix  Readings  ...... 

Error  Due  to  Dissolved  Mineral  Matter 
Determination  of  Ash  . 

Calibration  of  Saccharimeter-Scales  by  Control-Tube 
Quotient  of  Purity  ...... 

References  ........ 

Tables 

Recipes,  etc 


15 

16 

17 

18 

18 

19 

20 

21 

21 

22 

22 

23 

23 

24 

25 

25 

25 

26 

28 

29 

30 

32 


I.  SYNOPTIC  LECTURE  NOTES  IN 
SUGAR  ANALYSIS. 

EARLIER  HETHODS. 

Difficulties  in  determining  cane-sugar  by  the  usual  analyt- 
ical methods.  Four  processes  of  limited  application  not 
meeting  commercial  requirements : 

(1)  Fermentation  by  Yeast. — (a)  By  action  of  the 

invertase  ; C12  H22  On  + H2  O = 2 C6  H12  06.  (b)  By 

fermentation;  C6  H12  06  = 2 C 02  + 2 C2  H5  O H. 
Objections  — Long  time  required.  Action  of  foreign  fer- 
ments. 

(2)  Inversion  and  Titration  with  Fehling  Solution. — 
Treatment  with  hydrochloric  acid.  Preparation  and  manip- 
ulation of  Fehling  solution  in  volumetric  method.  Cu2  O 
precipitated.  Conditions  affecting  accuracy.  Time  of  boil- 
ing— dilution.  Soxhlet’s  modification.  Gravimetric  methods 

— Cu  O or  Cu2  O weighed  (O’Sullivan),  Cu  (Allihn),  Cu 
by  electrolysis  (Wiley). 

(3)  Specific  Gravity  at  standard  temperature , 17.5°  C. 

— Balling-Brix  hydrometers.  Only  accurate  where  soluble 
impurity  is  small.  Valuable  in  commercial  work  in  connec- 
tion with  other  methods. 

(4)  Extraction  by  Alcohol. — Accurate,  but  only  appli- 
cable to  substances  containing  small  quantities  of  sugar. 
Sugar  weighed  directly. 

OPTICAL  ANALYSIS. 

General  Principles. — Biot,  1815,  discovered  action  of 
solutions  of  sugar  and  certain  other  organic  substances  on 
polarized  light  rays.  Double  refraction  caused  by  some 
crystals.  Iceland  spar.  Suppression  of  one  member  of 
doubly  refracted  ray  by  Nicol  prism.  Passage  of  light 
through  two  Nicol  prisms  in  succession,  (a)  edges  of  end 


6 


faces  parallel ; (b)  edges  at  right  angles.  Characteristics  of 
Polarized  Light  Beam , Essential  to  its  Use  in  Optical 
Analysis  (as  shown  by  its  passage  through  two  Nicol  prisms 
in  succession).  (1)  A beam  of  given  intensity  can  pass 
only  at  a definite  position  of  the  prisms  relative  to  each 
other.  Interpretation  by  wave  theory.  Diagrams  : ordinary 
light  beam,  polarized  beam.  Conclusion  of  Theory : That 
a polarized  light  beam  can  be  considered  as  having  its  vibra- 
tions in  one  plane  (“plane  of  polarization”)  whose  direc- 
tion in  space  bears  a constant  relation  to  the  principal  section 
of  the  Nicol  prism.  (2)  Rotation  of  beam  by  sugar  solution. 
How  shown. 

Angle  of  rotation  (a)  proportional  to  concentration  (c), 
distance  traversed  through  solution  (Z),  and  varies  with  the 
color  of  the  light  ray,  the  proportional  effect  on  each  color 
being  the  same  as  that  caused  by  the  dispersion  of  the 
solution.  The  angular  degrees  of  rotation  of  the  polarized 
ray  of  standard  color  caused  by  one  gram  of  the  optically 
active  substance  dissolved  in  each  cubic  centimeter  of  solution 
in  a column  one  decimeter  long  are  taken  as  a measure  of  the 
Specific-Potatory  Power  (a)  of  that  substance.  The  Funda- 
mental Formula  expressing  rotation  of  the  polarized  ray  by 
any  optically-active  substance : a — ale  when  (a)  is  angle 
of  rotation  in  degrees , (l)  — length  of  column  in  decimeters 
and  (c)  = concentration  of  the  solution  of  (w)  grams  of 
optically-active  substance  in  (v)  cubic  centimeters  of  solution. 

w alw  , av  ^r,  / N . i 

c — - .*.  a — and  a = — . When  (c)  is  expressed  as 

V V Iw 

per  cent  of  substance  in  solution  the  density  (d)  must 

be  known,  - = .-.  a = [Note  carefully  the  dis- 

v 100  Ipd 

tinction  between  grams  in  100  cubic  centimeters  and  grams  in 

100  grams  of  solution.]  For  liquids  not  requiring  solvents, 

- = \ where  d — density  of  liquids,  a — tv  For  solid 
v d la 

sections,  as  quartz ; a — j,  l = 1 millimeter.  When  stan- 
dard yellow  light  (D)  ray  of  spectrum)  is  used,  a is  expressed 


7 


[a]D;  when  “mean  yellow”  light  is  used  (measured  by 
observation  of  its  complementary  “ transition-tint  ”) , [a]J# 
Constancy  of  a affected  in  some  cases  by  variations  in 
temperature,  concentration,  and  nature  of  solvent,  a of 
cane-sugar  practically  constant  under  ordinary  conditions  of 
laboratory  practice.  Standard  temperature,  17.5°C  (more 
recently,  20°). 


APPLICATION  OF  PRINCIPLES  TO  SUGAR  ANALYSIS. 

w'  — weight  of  sample,  w — weight  of  sugar  in  sample 
w • . av  _ av 

••  Vr  = % suSar  W = aV  % = 5S5>- 


POLARISCOPES. 

Essential  parts  ; polarizer,  tube  for  solution,  rotating  ana- 
lyzer with  scale  for  measuring  angle  of  rotation,  optical 
device  for  determining  exact  position  of  plane  of  polariza- 
tion relative  to  the  analyser,  source  of  light  necessarily 
monochromatic.  Early  polari scopes  used  day  or  lamp  light 
getting  monochromatic  effect  by  “transition-tint”  plate, 
giving  [a]j.  Now,  all  polariscopes  in  common  use  employ 
sodium  flame  filtered  through  potash  bichromate.  This  gives 
light  closely  approximating  to  D ray,  giving  [«]D.  Landolt 
and  other  German  scientists  filter  sodium  light  through  a 
Lippich  “ray-filter”,  (1)  potash  bichromate,  (2)  uranium 
sulphate.  This  gives  a closer  approximation  to  D ray  and 
consequently  constants  of  slightly  different  value.  End- 
point devices  giving  shade  comparisons.  — Jellet-Cornu 
(“split”)  prism,  planes  of  polarization  making  a slight  angle 
with  each  other  in  each  half  of  the  field.  How  used.  Dis- 
advantages : Relationship  of  angle  of  planes  of  polarization 
to  sensitiveness,  to  intensity  of  light.  Laurent’s  half  disc  and 
rocking  polarizer.  Advantages  gained  : The  most  desirable 
instrument  today.  Landolt-Lippich  polariscope  uses  small 
Nicol  prism  in  one-half  of  field  in  front  of  polarizer  instead 
of  half-disc  of  quartz.  The  Wild  “ polaristrobometer.” 
End  point : Disappearance  of  interference  fringes  made  by 
Savart  polariscope ; polarizer  rotates  and  carries  scale ; 
inconvenient  but  accurate. 


8 


EVOLUTION  OF  THE  SACCHARIHETER. 

Commercial  demand  for  an  instrument  giving  a direct 
reading  of  per  cent  of  sugar  in  sample  without  necessity  of 
calculation.  Necessary  conditions  (1)  l,  v , and  w,  constants 
(2)  when  w = w',  a = 100  divisions  of  scale.  .*.  (When  w 
— any  weight  of  pure  sugar  in  w'  of  a sample)  w : w'  = R 
(the  scale  reading)  : 100.  In  “ saccharimeters,”  1 — 2 
decimeters,  v — 100  cubic  centimeters.  The  fixed  value  of 
w'  always  taken  for  solution  depends  on  graduation  of  the 
scale,  and  is  known  as  “normal  weight,”  (N).  General 
formula  for  calculation  of  per  cent  when  other  than  the 

N 

normal  weight  is  used  : % = R — . 

w' 

Saccharimeter  Scales.  Calculation  of  N for  scale  of  angu- 
lar degrees  when  1 — 2 and  v = 100.  Objectionable  size  of 
weight.  Duboscq  scale,  a = rotation  of  yellow  ray  caused 
by  a millimeter  section  of  “right-handed”  (dextro-rotary) 
quartz  cut  perpendicular  to  the  optical  axis.  N = 16.35g. 
Same  scale  used  by  Laurent.  More  modern  scale,  N = 
16.19g. 

Quartz-wedge  Saccharimeters , Inconvenience  of  sacchari- 
meters with  rotating  analysers  on  account  of  the  necessity 
of  monochromatic  light.  The  Soleil  quartz-wedge  compen- 
sator, measures  the  thickness  of  a section  of  “left-handed” 
(lsevo-rotary)  quartz  necessary  to  neutralize  the  dextro- 
rotary  action  of  the  sugar  solution.  Independent  of  the 
source  of  light,  since  the  dispersive  power  of  quartz  and 
sugar  solutions  are  almost  exactly  equal.  On  this  account 
the  thickness  of  the  quartz  section  necessary  to  restore  the 
position  of  the  plane  of  polarization  of  any  ray  bears  a con- 
stant relation  to  the  concentration  of  the  sugar  solution  which 
originally  displaced  it.  Limitations  to  sensitiveness  of  the 
Soleil-Duboscq  saccharimeter,  owing  to  the  small  size  of  the 
normal  weight.  Ventzke’s  scale  : 100  point,  originally  the 
rotation  caused  by  a solution  of  cane-sugar  of  1.100  Sp.  Gr. 
This  now  taken  as  equivalent  to  N = 26.048g.  Function 
of  “ sensitive-tint  producer.”  Details  of  instrument  much 
improved  by  Scheibler  and  known  as  Soleil-Ventzke- 


9 


Scheibler.  This  saccharimeter  used  more  than  any  other  in 
commercial  work.  Objections : Use  prevented  by  color- 
blindness. Sensitiveness  much  decreased  by  dark,  highly- 
colored  solutions.  Gradually  being  superceded  by  the 
Schmidt  and  Haensch  ‘ ‘ Half-shade  ” modification  of  end- 
point by  use  of  Jellet-Cornu  prism.  This  instrument  in  use 
by  the  Am.  Sug.  Rfys.  Co.  and  the  U.  S.  Dept,  of  Agri- 
culture. Latest  device  gives  a triple-shade  field  by  an 
end-point  device  on  the  principle  of  the  Lippich  polariscope, 
— combination  of  three  Nicol  prisms — said  to  have  increased 
sensitiveness. 

SOURCES  OF  ERROR  IN  “POLARIZATIONS.” 

(w')  weighings  to  0.005  gram  sufficiently  exact.  ( l ) 2 
decimeter  tubes  exact  to  0.1  millimeter.  ( v ) 100  cubic- 
centimeters  to  0.05  cubic-centimeter ; — 1 cubic-centimeter  = 
volume  of  1 gram  of  water  weighed  in  air  at  17.5°C, 
employed  in  graduation  of  all  instruments  in  common  use 
in  this  country.  Recent  German  saccharimeter s standard- 
ized for  true  cubic-centimeters,  where  1 cc  = volume  of  1 g 
of  water  weighed  in  vacuo  at  4°C. 

Errors  of  Instrument.  (1)  (Rotary)  Eccentricity  of 
axes  of  scale  and  rotation.  Corrected  by  readings  in  oppo- 
site quadrants.  (2)  Distortion  of  cover-glasses  of  tubes  by 
pressure  — screwing  caps  too  tightly.  Practically  impos- 
sible in  tubes  as  now  constructed.  Landolt’s  tubes. 
Laurent’s  (3)  Errors  of  graduation  calculated  for  by  standard 
quartz-plate  readings  and  calibration  by  “control  tube.” 

(4)  “Zero-error,”  — plus  or  minus  constant  correction. 

(5)  Errors  of  observation  eliminated  by  averaging  results. 

(6)  Variations  from  standard  temperature:  Error  in  most 
cases’,  slight.  Corrections  by  tables  of  Wiley,  Andrews, 
and  Mategczek.  Effects  of  temperature  variation  complicated 
and  obscure. 

OTHER  COMilON  DETERHINATIONS  OF  SUGAR  ANALYSIS. 

Moisture.  No  exact  rapid  method  for  drying  sugars  and 
syrups  known,  owing  to  decomposition.  Attempts  to 
obviate  this  by  vacuum-apparatus,  drying  in  current  of 
hydrogen,  etc.  of  doubtful  success.  Standard  Commercial 


10 


Method : Soak  up  dilute  solution  of  syrup  by  sand  and  dry 
at  105°C.  till  loss  is  not  greater  than  .2%  per  hour.  Ash 
obtained  in  usual  manner  by  ignition  in  platinum  dish  at 
dull-red  heat.  Difficult,  owing  to  light  bulky  coal  formed  in 
burning.  Obviated  somewhat  by  admixture  of  vaselin  or 
pure  benzoic  acid.  Standard  Commercial  Method  : Treat- 
ment with  concentrated  sulphuric  acid  before  ignition  and 
making  an  arbitrary  deduction  of  10%  of  weight  of  ash  to 
allow  for  excess  due  to  formation  of  sulphates. 

“ Reducing  Sugars ” by  volumetric  Fehling  method  which 
is  sufficiently  accurate  owing  to  the  relatively  small  amount 
of  these  sugars  present. 

APPLICATION  OF  POLARISCOPE  DETERHINATIONS  IN  THE 
ESTIMATION  OF  OTHER  SACCHARINE  SUBSTANCES. 

Honey,  Practically  pure  invert-sugar.  Usually  0.5  to  2 % 
cane-sugar  in  natural  honeys ; in  rare  cases  as  much  as 
4%.  Estimated  by  double  polarization.  Loevulose , by 
Wiley’s  method  based  on  the  change  of  rotation  caused  by 
temperature.  Variation  for  one  gram  in  100  cc  is  .0357° 
( S.  & H.)  or  .0126°,  D per  degree  C.  Specially  devised 
tubes  necessary  for  reading  the  solution  at  a high  and  low 
temperature.  Principal  adulterations  of  honey ; commercial 
glucose  and  cane-sugar. 

Lactose.  Method  analagous  to  cane-sugar  determination, 
using  a normal  weight  proportional  to  the  specific  rotatory 
power  of  lactose.  N = 32.91g,  when  v — 100  and  1 — 2 
for  S.  and  H.  saccharimeter.  Acid-mercuric  nitrate  is  used 
for  a clarifying  agent.  Correction  must  be  made  for  the 
volume  of  precipitated  casein  by  method  of  “ double  dilu- 
tion a — reading  when  v — 100,  5,  the  reading  when  v — 

200.  Then,  the  true  reading  is  — °^—r. 

a — b 

ANALYSIS  OF  COMMERCIAL  GLUCOSE. 

Viscid,  colorless,  highly  concentrated  and  refined  solution 
(75-85%)  of  maltose,  dextrose,  and  dextrin  with  trace  of 
albuminoids  and  oil,  0.3  — 0.4%  mineral  matter. 

Three  determinations  necessary  in  analysis  : ( 1 ) Total 

carbohydrates  (anhydrous)  by  Brix  spindle  or  specific-gravity 


11 


apparatus,  corrections  being  made  for  influence  of  mineral 

matter  (“  ash”).  (2)  “ Cupric  Reducing  Power”  (/T)  = 

copper  reduced  by  1 gram  of  carbohydrate  . , .. 

— — ? ’ 7 , — — - — tt-7 — , by  h ehling  gravi- 

copper  reduced  by  1 gram  of  dextrose 

metric  methods  : (a)  Allihn’s  method  by  reducing  to  copper ; 
(b)  Wiley’s  modification  by  electrolysis;  (c)  Defren’s  modi- 
fication of  O’Sullivan’s  copper-oxide  determination. 

(3)  Specific  rotatory  power  : [a]D.  Solution  must  be  pre- 
viously heated  to  boiling,  to  obviate  possible  influence  of 
“ birotation.”  All  constants  used  in  calculation  and  values 
obtained  are  referred  to  a weight  of  anhydrous  carbohydrate 
calculated  from  the  density  of  the  solution,  on  the  assump- 
tion that  this  density  corresponds  to  a concentration  identical 
with  that  of  a cane-sugar  sugar  solution  of  same  density. 
Calculation  of  Analytical  Results:  If  g = % dextrose,  m = 
% maltose,  and  d — % dextrin : 

(1)  ^ + m + d — 1. 

(2)  g + .61m  = K. 

(The  cupric  reducing  power  of  maltose  being  .61  that  of 
dextrose.) 

(3)  53.5 g + 135.2 m + 195d  = a . 

(These  figures  giving  a of  dextrose,  maltose,  and  dextrin 

respectively. ) 

a + 141. 5&  — 195 

m ~ 26.52 

g — K — .61m 
d z=z  1.00  — m ■ — g 

This  method  gives  correct  proportional  amounts  of  these 
carbohydrates  per  unit  of  anhydrous  glucose,  not  the 
absolute  weights. 


ANALYSIS  OF  WORTS  AND  MALT  SYRUPS  WHEN  RESULT- 
ING FROM  ACTION  OF  DIASTOSE  ON  STARCH  ALONE. 

Identical  methods,  but  since  maltose  and  dextrin  alone  are 
present : 

m -f-  d — 1 
.61m  = K 

135.2m  + 195c?  = a . 

Obviously  two  equations  only  are  necessary. 


12 


II.  LABORATORY  MANIPULATION. 

GENERAL  NOTES  AND  DIRECTIONS  APPLYING  TO 
SACCHARinETERS  AND  POLARISCOPES. 

CARE  OF  EYESIGHT. 

Before  taking  readings,  be  satisfied  that  the  field  is  as 
evenly  and  brightly  illuminated  as  possible,  and  the  image 
of  the  field  sharply  focussed.  See  that  the  illuminating 
apparatus  of  the  scale  is  in  proper  order.  To  adjust  focus 
and  illumination  in  shadow  instruments,  turn  the  scale  some 
divisions  from  zero  to  get  full  volume  of  light.  Practice 
several  rapid  readings,  averaging  the  results  rather  than 
fatigue  the  eyes  by  long  operations.  The  shorter  readings, 
if  conscientiously  made,  are  more  accurate.  End-point. 
Move  the  shadow  slightly  from  one  side  of  the  field  to  the 
other  several  times,  confining  attention  to  the  central  vertical 
line.  Take  the  point  of  transition  across  this  line  as  the 
end-point.  This  is  theoretically  identical  with  the  point  of 
even  illumination  of  the  field,  but  it  is  easier  to  locate  end- 
point in  the  former  manner,  since  often  through  dust,  imper- 
fect adjustment  of  prism  or  other  defect,  poor  illumination, 
uneven  dispersion  in  wedge  instruments,  etc.,  it  may  be 
impossible  to  get  both  halves  of  the  field  to  look  exactly 
alike.  Turn  scale-lights  off  immediately  after  using,  as  the 
glare  quickly  impairs  sensitiveness  of  vision. 

In  beginning  work  with  an  unfamiliar  instrument,  set  scale 
to  zero  and  study  the  changes  in  the  field  about  this  point. 
This  is  better  than  hunting  blindly  for  what  you  may  not 
recognize,  with  possible  injury  to  eyesight  and  instrument. 
It  is  especially  important  when  some  unusual  end-point  is 
observed,  as  in  the  Wild  polariscope. 

CARE  OF  INSTRUMENT. 

Like  many  instruments  of  precision,  polariscope  appar- 
atus is  extremely  sensitive  to  derangement  from  shocks 
caused  by  careless  handling.  Instruments  should  be  dis- 
turbed as  little  as  possible,  except  in  the  usual  manipula- 
tion of  testing.  Mcol  prisms  from  the  nature  of  their 
material  (calc-spar)  are  peculiarly  liable  to  injury.  Calc- 
spar,  being  much  softer  than  glass,  is  easily  scratched  by 
careless  handling  or  cleaning.  Its  peculiar  crystallization 


13 


makes  it  liable  to  split  from  rapid  changes  in  temperature, 
or  in  overheating  by  placing  instrument  too  close  to  the 
lamp.  It  is  easily  corroded  by  acids  caused  by  the  fermen- 
tation of  sugar  solutions  carelessly  spilled  in  the  trough  of 
the  instrument.  With  proper  care  polarizing  apparatus  will 
last  a lifetime.  As  the  accuracy  of  the  sugar-chemist’s 
work  is  so  dependent  on  the  precision  of  the  instrument, 
daily  practice  in  such  care  as  will  insure  this  precision  is  a 
necessary  part  of  the  knowledge  and  duties  required  of 
every  worker  in  a sugar-laboratory.  Handle  the  instru- 
ment with  clean  hands.  See  that  the  flame  of  the  lamp  is 
about  200  millimeters  from  the  front  end  of  the  instrument, 
the  length  of  an  ordinary  polariscope  tube.  This  avoids 
overheating,  which  not  only  endangers  the  prisms  but 
throws  the  instrument  out  of  adjustment.  With  most  types, 
it  also  insures  an  evenly  illuminated  field  of  maximum 
brightness.  Only  when  necessary  clean  lenses,  quartz- 
plates  and  cover-glasses  with  absolutely  clean  filter-paper  or 
linen  cloth,  never  with  silk  or  chamois,  as  the  rough  sur- 
faces of  these  fabrics  are  liable  to  hold  grit.  Always  rub 
very  lightly.  In  case  the  edges  cannot  be  reached,  remove 
dirt  very  carefully  with  a clean  pointed  stick  of  soft  wood, 
as  a tooth-pick.  Clean  Nicol-prisms  with  especial  care,  and 
only  when  absolutely  necessary.  In  the  best  instruments, 
Nicol  prisms  are  enclosed  in  glass. 

POLARISCOPE=TUBES. 

Before  placing  tubes  in  trough,  carefully  wipe  away  all 
traces  of  solution  or  other  accidental  moisture,  and  avoid 
hitting  tube  Against  scale  or  other  delicate  part.  In  placing 
caps  on  polariscope-tubes,  note  that  the  number  (or  symbol) 
corresponds  with  that  on  the  end  of  the  tube.  This  will 
insure  a tight  tube,  and  prevent  jamming  or  sticking  of  the 
caps.  All  apparatus  that  has  been  in  contact  with  solu- 
tions should,  immediately  after  using,  be  washed  inside  and 
out  in  running  water  and  placed  in  rack  to  dry.  This  rule 
is  necessary  to  insure  a constant  supply  of  clean,  dry  appar- 
atus. Take  care  to  wash  the  brass-work  at  the  ends  of  the 
tubes,  as  this  prevents  caps  from  sticking.  After  washing, 
leave  cover-glasses  out  to  facilitate  drying ; but  place  caps 


14 


on  ends  of  tubes,  so  as  to  protect  ground-glass  surfaces 
from  chipping  by  any  accident.  The  lead  in  sugar  solutions 
gradually  clouds  glass-ware.  Remove  by  occasional  wash- 
ing with  hydrochloric  acid.  If  cover-glasses  stick  in  caps, 
force  them  out  with  a stick  of  wood  (not  of  metal  or  glass.) 
[See  also  under  Polarization  of  Sugar  Samples. ] 

Scale-Readings . — Always  correct  readings  for  zero-error 
(the  difference  between  the  end-point  observed  as  read  on 
the  scale  and  the  zero  of  the  scale)  noting  whether  this  is 
+ or  — . 

In  case  zero-error  is  not  large,  it  is  better  to  allow  for  it 
in  calculations  than  to  attempt  to  bring  the  scale  into  perfect 
adjustment. 

Take  the  average  of  six  readings  for  all  exact  work, 
rejecting  the  first  reading  if  it  shows  much  discrepancy  from 
the  others. 

All  saccharimeter  scales  are  read  and  expressed  in  per- 
centages and  tenths.  Rotary  polariscopes  give  readings  in 
degrees  and  minutes.  In  calculations  the  minutes  are 
expressed  as  decimals  of  a degree.  Saccharimeter  scales 
are  divided  into  per  cent  divisions,  rotary  scales  either  into 
halves  or  thirds  of  a degree.  In  both  cases  the  fractions  of 
these  divisions  are  determined  by  “verniers.”  A vernier 
(so  called  from  the  inventor,  a French  mathematician)  is  a 
double  sliding  scale  extending  in  both  directions  from  a 
zero-mark,  each  half  of  which  has  a length  in  divisions  of 
the  main  scale  one  less  than  the  number  of  parts  into  which 
it  divides  the  division,  but  this  length  of  vernier  is  itself 
divided  into  a scale  of  just  the  number  of  parts  that  the 
vernier  divides  the  main  scale  division.  For  instance,  a 
vernier  to  divide  a scalerdivision  into  ten  equal  parts  is 
itself  nine  scale-divisions  long  and  divided  into  ten  equal 
parts.  Hence  each  division  of  the  vernier  is  of  the 
original  scale  division.  Starting  from  the  zero  on  the 
vernier,  and  going  in  the  direction  of  the  scale  reading , the 
number  of  the  line  of  the  vernier  which  coincides  with  a line 
on  the  main  scale  gives  the  number  of  the  parts  of  the  scale- 
division  which  the  index  (zero  of  vernier)  marks.  Hence, 
in  the  case  of  a vernier  reading  tenths,  if  the  zero  of  the 


15 


vernier  lies  beyond  the  sixth  division  and  the  ninth  line  of 
the  former  coincides  with  a line  of  the  main  scale  the  read- 
ing: would  be  6.9  divisions.  When  the  zero  of  the  vernier 
lies  on  the  minus  side  of  the  scale  the  lines  on  the  corres- 
ponding side  of  the  vernier  are  read.  On  rotary  scales, 
verniers  usually  read  to  even  minutes  only,  half  degree 
divisions  being  divided  into  fifteen  parts,  thirds  of  degree 
divisions  into  ten  parts.  In  reading  rotary  scales  the 
number  of  divisions  marked  by  the  zero  of  the  vernier  is 
first  read,  and  then  expressed  in  degrees  and  minutes.  Not 
until  this  is  done  should  the  vernier  be  read  and  its  reading 
added.  Study  system  of  division  till  you  thoroughly  under- 
stand it  before  taking  readings. 

NOTES  APPLYING  TO  SPECIAL  INSTRUHENTS. 

Schmidt  & Haensch  Half- Shade  Saccharimeter . — w'  = N 
^=26.048^,  when  v = 100  and  l = 2.  -j-  readings  to  right. 
Vernier  reads  to  0.1%. 

Laurent  polariscope. — {Half- Shade.)  Rotary  scale, 
vernier  reads  to  2'.  Sugar-scale,  vernier  reads  to  0.1%. 
t0'=:N  when  1 — 2 and  v — 100  (N  to  be  determined  by 
quartz-plate  comparisons  with  S & H saccharimeter).  See 
that  flames  of  lamp  are  properly  adjusted  and  that  platinum- 
gauze  baskets  have  their  edges  parallel  to  but  not  touching 
flame-cones.  Add  new  salt-paste. every  five  or  ten  minutes. 
Swing  instrument  till  it  points  at  the  flames.  Turn  the 
analyser  off  from  zero,  and  focus  image  of  half  disc  sharply 
with  eye-piece.  Turn  the  analyzer  to  zero,  and  raise  lever 
on  left,  behind  the  scale  as  high  as  it  will  go,  or  as  will  let 
just  light  enough  pass  to  form  a well-defined  image.  This 
gives  maximum  sensitiveness.  Determine  zero-error  at  0 
and  180°,  when  construction  of  instrument  admits  ( + , in 
direction  of  the  going  of  the  hands  of  a clock.)  If  eccen- 
tricity is  less  than  2',  readings  in  the  opposite  quadrant  can  be 
dispensed  with.  Avoid  turning  adjustment-pinion  on  the 
eye-piece  tube,  as  this  throws  the  prism  out  of  adjustment 
with  the  scale.  This  instrument,  adopted  by  French 
Government  for  su^ar  testing:. 

o o 

Soleil-Duboscq  Transition-Tint  Saccharimeter. — ( -f-read- 
ngs  to  left.)  Scale  shows  % of  pure  sugar  when  w'  — AT, 


16 


l = 2,  and  v = 100  (N  to  be  determined  by  quartz-plate 
comparisons  with  S.  and  H.  saccharimeter.)  Read  to  0.1 
% by  estimation , as  the  scale  has  no  vernier.  See  that 
image  is  properly  focussed  by  moving  eye-piece.  (Moves 
in  slot.)  Set  scale  to  zero  by  pinion  below  the  wedges 
before  looking  through  instrument.  Turn  milled  head  in 
eye-piece  (which  has  a movement  through  half  & circle)  till 
color  is  almost  white,  then  adjust  color  to  a very  pale  tint 
(usually  a pearl  or  a flesh  tint)  best  suited  to  your  eye  for  a 
back-ground  for  showing  the  pale-rose  transition  tint  which 
appears  in  one-half  of  the  field  when  the  scale  is  not  quite 
at  zero.  True  zero  is  the  point  at  which  both  halves  of  the 
field  have  the  same  weak  color  which  changes  at  the 
slightest  movement  of  the  quartz- wedges,  showing  rose  in 
one-half  and  its  complementary  (green)  in  the  other.  If 
the  milled  head  which  turns  the  eye-piece  prism  (“sensitive 
tint  producer  ” ) is  adjusted  to  too  strong  a tint,  the  sensi- 
tiveness of  the  instrument  is  greatly  decreased.  When  a 
tube  containing  a solution  is  placed  in  the  instrument  the 
tint-producer  must  be  readjusted  till  a sensitive  tint  is  again 
obtained.  Reading  by  noting  transition  of  tint  across  cen- 
tral line,  as  in  case  of  shadow  instruments,  is  recommended. 
Keep  the  hood  as  dark  as  possible  and  avoid  looking  at 
bright  lights  before  reading,  as  this  causes  the  eye  tempor- 
arily to  lose  its  power  of  distinguishing  delicate  shades. 
For  same  reason  avoid  fatiguing  the  eye  by  looking  at  the 
image  for  more  than  a few  seconds.  Frequent  quick  read- 
ings give  the  best  results.  With  most  observers  readings 
agree  only  within  0.3  to  0.5%.  On  this  account  this 
instrument  is  rarely  used  now  in  commercial  work. 

Soleil-  Ventzke- Scheibler  Transition-Tint  Saccharimeter . 
A much  improved  and  more  sensitive  form  of  transition-tint 
saccharimeter.  The  most  common  commercial  instrument 
in  use  in  America  and  Germany.  Wedges  and  scale  iden- 
tical with  S.  and  H.  saccharimeter  (W  = 26.048g.)  Sensi- 
tive-tint producer  in  front  of  polarizer  and  worked  by 
milled-head  on  long  spindle  at  right  of  eye-piece.  Notes 
on  manipulation  of  Soleil-Duboscq  saccharimeter  apply  to 
this  instrument,  which  has  identical  optical  parts.  Easily 
reads  to  0.1%  by  vernier. 


17 


SUGAR  LABORATORY  EXERCISES.  MASS.  INSTITUTE 
OF  TECHNOLOGY. 


(15 

hour  course.) 

No. 

Determination. 

Instrument. 

Test  Used. 

I. 

1°S  & H 

IV 

Laurent  (A  or  C) 

S & H (B  or  D) 

Quartz-Plate 
(A  or  B) 

II. 

l°s  & H 

IV 

Laurent  (A  or  C) 

S & H (B  or  D) 

Any  commercial  glu- 
cose solution  of  about 
10%  in  2dm.  tube. 

III. 

N of  Laurent. 

Laurent  (A  or  C) 

S & H (B  or  D) 

Any  Quartz-Plate. 

• 

IV. 

N of  Soleil-Duboscq. 

S-D  (E) 

S & H (B  or  D) 

Any  Quartz-Plate. 

v; 

Polarization  of  three 
samples  of  raw  sugar. 

Each  on  S & H 
(B  or  D) 

1 

VI. 

VII. 

Readings  of  each  tube 
on  two  instruments. 

Use  calculated  normal 
weights  Make  up  one 
tube  of  solution  from 
each  sample. 

Two  on  Laurent 
(A  or  C) 

One  on  S-D 
(E) 

Any  sample  of  raw 
sugar  (except  second 
sugars.) 

VIII. 

[«]d386  of  Commer- 
cial Glucose. 

S & H (B  or  D) 

| (Use  data  from  II. 
jL-  by  Brix  spindle.) 

Any  sample  of  com- 
glucose  diluted  to 
10%  solution. 

IX. 

[a]  D of  Tartaric  Acid. 
(Plot  values,  and  cal- 
culate absolute  spe- 
cific rotatory  power 
roughly.) 

Laurent  (A) 

1 = 4 or  5 

C.  P.  Tartaric  Acid 
three  solutions, 
c = 5 c = 10  c = 20 

IX  (alter- 
nate.) 

[a] d of  Amyl 
Alcohol. 

! Laurent  (A) 

(1  = 4 or  5) 

Com.  Amyl  Alco- 
hol. (Take  sp.  gr. 
by  pyknometer. 

X. 

Double  Polarization 
by  Clerget’s  Method. 

S & H (B  or  D) 

1 

Any  Molasses  or 
2nd  sugar. 

XI. 

Calibration  of  S -f-  H 
by  control-tube. 

S & H (B  or  D) 
using  control-tube. 

J Granulated  sugar. 

1 

XII. 

Quotient  of  purity. 
Calculation  of  form- 
ula for  determining  % 
of  sugar. 

S & H (B  or  D) 

“ Total  Solids  ” by 
Brix  spindle. 

Any  2nd  sugar 
or  molasses  diluted 
to  about  10%. 

Th q printed  blanks  provided  should  be  filled  in  duplicate 
for  each  determination  (12  in  all)  giving  all  data.  The 
right  half  is  for  the  instructor,  the  left  being  retained  by  the 
student  for  filing  in  his  note-book.  Calibration  tables,  plots, 
etc.,  can  be  placed  on  back  of  blanks. 


18 


QUARTZ-PLATE  COMPARISONS. 

Standard  quartz-plates  of  known  rotation  are  usually 
employed  to  determine  the  values  and  correctness  of  the 
graduation  of  the  scales  of  instruments.  In  this  laboratory 
they  are  used  to  determine,  (1)  The  equivalent  of  one 
division  of  the  S.  & H.  saccharimeter  in  angular  degrees  of 
rotation  of  the  D ray;*  (2)  The  normal- weight  of  the 
Laurent  saccharimeter  by  comparison  with  the  S.  & H. 
scale  of  known  normal- weight  (26.048g)  ; (8)  The  normal 
weight  of  the  S.  D.  saccharimeter  by  comparison  with  the 
S.  & H.  scale. 

Take  readings  as  near  20°  C as  possible.  Record  tem- 
perature, so  that  corrections  can  be  made  if  necessary. 
The  changes  of  specific-rotatory  power  of  the  quartz-plate 
from  variations  of  temperature  are  compensated  for  by  a 
similar  change  in  the  quartz-wedges  of  the  saccharimeter. 
The  other  effects  of  change  in  temperature  are  complex  and 
indeterminate,  but  in  most  cases  of  ordinary  work  negligible, 
even  in  rotary  instruments  unless  the  variation  from  20°  is 
considerable.  Quartz-plates  should  always  be  placed  in  the 
instrument  in  the  position  indicated  by  a mark  or  stud  on 
the  mounting,  since  they  are  rarely  ground  so  perfectly  as  to 
read  the  same  in  every  position.  [In  this  laboratory  quartz- 
plates  are  read  with  the  mark  ( x ) at  the  top  of  the  mount- 
ing, the  end  holding  the  quartz  facing  the  observer.]  Many 
of  the  recent  German  quartz-plates  read  higher  than  their 
recorded  figures,  as  they  are  standardized  for  instruments 
with  graduations  based  on  a normal  weight  of  26.048g  of 
sugar  in  100  true  cubic-centimeters,'  (1  cubic  centimeter 
being  the  volume  occupied  by  one  gram  of  water,  weighed 
in  vacuo  at  a temperature  of  4°  C.) 

VALUE  OF  DIVISIONS  OF  SACCHARIMETER  SCALE  IN 
ANGULAR  DEGREES  BY  COMPARISON  HADE 
WITH  A TEN  PER  CENT  COMHERCIAL 
GLUCOSE  SOLUTION. 

Make  comparisons  between  readings  of  Laurent  polari- 
scope  and  S.  & H.  saccharimeter  precisely  as  with  quartz- 

*A11  results  expressed  for  “D  ray”  are  obtained  by  the  sodium  light  filtered 
through  potash  bichromate.  They  differ  slightly  from  those  values  obtained 
by  the  Lippich  ray-filter  which  is  said  to  give  a closer  approximation  to  the 
true  D ray.  The  former  method,  however,  furnishes  the  light  standard 
generally  adopted. 


19 


plates,  using  tube  containing  a solution  of  commercial 
glucose  of  approximately  ten  per  cent.  The  value  obtained 
differs  slightly  from  that  got  with  quartz-plate,  since  the 
quartz  wedges,  having  a slightly  different  dispersive  power 
from  the  glucose,  will  not  restore  each  rotated  ray  quite  to 
its  original  position.  This  is  also  shown  by  the  fact  that 
when  the  glucose  solution  is  read  in  the  saccharimeter,  the 
two  halves  of  the  field  at  the  end-point  have  weak  contrast- 
ing tints.  This  determination  suggests  the  limitations  of 
the  quartz-wedge  saccharimeter  in  general  scientific  work,  as 
it  can  be  used  only  when  the  dispersion  of  the  solution 
measured  approximates  closely  to  that  of  quartz.  In  every 
case  the  value  of  the  divisions  of  the  saccharimeter  in 
angular  degrees  of  rotation  of  yellow  light  should  be 
determined  by  comparisons  made  with  solutions  of  the 
substance  approximately  at  the  concentrations  to  be  used  in 
subsequent  investigations,  (a)  in  such  cases  obviously  being 
the  reading  of  the  saccharimeter  multiplied  by  the  ratio 
obtained.  The  difficulty  in  reading  the  end-point  owing  to 
the  inequality  of  tint  can  be  obviated  by  the  use  of  a “ mono- 
chromatic” eye-piece  which  contains  a section  of  a potassium 
bichromate  crystal.  This  absorbs  the  blue  rays,  which  give 
the  most  trouble  in  reading. 

CALIBRATION  OF  FLASKS. 

Instruments  in  present  use  are  standardized  for  volumes  of 
lOOcc,  where  one  cubic  centimeter  is  taken  as  the  volume 
occupied  by  one  gram  of  water,  weighed  in  air  at  17. 5 "C. 
Hence,  all  flasks  should  be  calibrated  on  this  standard.  Weigh 
the  thoroughly  cleaned  and  dried  flask  to  0.0 lg.  Weigh 
again  when  filled  with  freshly  distilled  water  of  known 
temperature.  The  volume  of  the  flask  can  then  be  com- 
puted from  the  following  formula  : v = P^  [1  + .000025 

(t  — 17.5)]  where  (v)  = the  required  volume,  (P)  the 
weight  of  water  in  grams  up  to  the  mark,  at  (t)°  C,  ( d ) 
the  density  of  water  at  17.5°  C and  ( d ')  the  density  at  the 
temperature  of  weighing.  That  part  of  the  formula  in 
brackets  expresses  the  effect  on  the  volume  of  the  expansion 


20 


of  the  glass  of  the  flask  and  is  small  enough  to  be  omitted 
in  ordinary  calibration.  The  modification  of  this  procedure 
for  double-marked  flasks  is  obvious. 

POLARIZATION  OF  CANE=SUGAR  SAMPLES.  GENERAL 
COfinERCIAL  flETHOD. 

Mix  representative  sample  thoroughly.  In  these  labora- 
tory exercises,  weigh  15-20  grams  (instead  of  the  normal- 
weight  of  the  saccharimeter  used)  as  rapidly  as  possible , 
to  avoid  change  in  uniformity  of  sample  by  evaporation  or 
drainage.  Weigh  in  tared  German-silver  dish  provided  for 
the  purpose.  Return  the  remainder  of  sample  at  once  back 
into  covered  jar  or  box.  Pour  about  50cc  of  water  into 
dish  and  grind  up  crystals  with  the  little  pestle  provided,  till 
they  are  practically  dissolved.  Pour  solution  off  into  lOOcc 
calibrated  dash , avoiding  pouring  out  any  undissolved  sugar. 
Add  a little  more  water  to  dissolve  the  rest  of  the  sugar.. 
In  raw  sugars  there  is  usually  a slight  residue  of  insoluble 
matter,  usually  sand  or  dirt.  Wash  entire  contents  of  dish 
into  the  flask,  add  about  2cc  of  basic  lead  acetate , the 
amount  varying  with  the  nature  of  the  sugar,  and  make  up 
to  mark  with  water. 

If  foam  prevents  the  reading  of  the  meniscus,  add  a drop 
of  ether,  which  will  dissipate  it.  Shake  solution  up 
thoroughly  and  filter  through  a dry  filter  into  a dry  cylinder, 
rejecting  the  first  few  drops.  Cover  the  funnel  with  a 
watch-glass  to  prevent  evaporation.  The  filtrate  should  be 
clear,  not  necessarily  colorless.  Rinse  polariscope-tube 
twice  with  the  solution,  filling  half -full,  shaking  and  pour- 
ing away,  then  fill  completely.  Before  placing  tube  in  the 
instrument  wipe  carefully,  and  see  that  outside  of  cover- 
glasses  is  clean  and  free  from  moisture.  If  objects  cannot 
be  seen  clearly  and  without  distortion  when  looking  through 
the  tube,  it  must  be  refilled.  If  the  tube  is  handled  much,, 
the  heat  of  the  hand  will  sometimes  temporarily  disturb  the 
solution,  which  will  become  clear  in  a few  minutes  if  the 
tube  is  placed  in  the  instrument.  Dark  solutions,  as 
molasses,  sometimes  require  either  diluting  before  polarizing,, 
the  calculation  being  modified  accordingly,  or  the  use  of  a 


21 


one-decimeter  tube.  Sometimes  the  solution  is  decolorized. 
Place  a few  grams  of  prepared  bone-black  in  the  dry  filter. 
Reject  the  first  third  of  the  filtrate  (first  30cc.) 

To  highly  refined  sugars  (granulated  sugars)  add  only 
one  cubic  centimeter  of  lead  solution,  shake  and  add  a few 
cc  of  sodium  sulphate  or  chloride  to  remove  excess  of  lead. 
A cream  of  aluminum  hydrate,  made  by  precipitating  a 
concentrated  potash-alum  solution  with  ammonia  and  then 
adding  an  equal  bulk  of  the  alum  solution,  works  very  well 
with  very  dark  solutions,  as  well  as  those  of  highly  refined 
sugars*. 

DETERMINATION  OF  CANE=SUGAR  WHEN  OTHER  OPTI= 
CALLY= ACTIVE  SUBSTANCES  ARE  PRESENT  BY 
METHOD  OF  DOUBLE  POLARIZATION. 

Fundamental  Principles.  (A)  Cane-sugar  alone  of  the 
more  common  carbohydrates  with  which  it  is  associated  is 
hydrolyzed  (inverted)  by  hydrochloric  acid  when  this  treat- 
ment is  carried  out  according  to  certain  strictly  limiting 
conditions.  (B)  A definite  weight  of  pure  cane-sugar  by 
inversion  has  its  rotation  changed  by  a constant  number  of 
divisions  of  the  saccharimeter  for  a given  temperature. 
Hence  the  amount  of  change  of  rotation  of  the  normal 
weight  of  any  sample  containing  cane-sugar  will  be  pro- 
portional to  the  per  cent  of  sugar  it  contains  (i.  e.  in  the 
same  ratio  to  the  amount  of  change  in  the  normal  weight  of 
pure  sugar,  as  the  sugar  percentage  of  the  sample  is  to  100. 
(C)  As  the  specific-rotatory  power  of  lsevulose,  one  of  the 
products  of  the  inversion,  decreases  rapidly  as  the  tempera- 
ture increases,  this  change  of  rotation  must  be  calculated  for 
a standard  temperature.  (D)  As  the  amount  of  change  of 
rotation  (i.e.  the  algebraic  difference  between  the  polaris- 
cope  readings  before  and  after  inversion)  alone  is  the 
measure  of  the  cane-sugar  present,  and  since  this  sugar 
alone  is  changed  by  the  process, f the  rotatory  effects  of 

* The  bulk  of  the  precipitate  formed  by  clarifying  agent  is  so  small  as  to 
be  negligible)  in  ordinary  polarizations.  In  exact  polarizations  of  very  low 
grade  products  the  reading  should  be  corrected  for  by  Scheibler’s  method 
of  Double  Dilution  [See  Lecture  Notes  : Determination  of  Lactose.] 

fWhen  considerable  quantities  of  commercial  glucose  are  present,  a slight 
correction  based  on  a formula  of  Weber  and  McPherson  (J.  Am.  Chem. 
Soc.  17.319),  and  amounting  to  a few  tenths  of  one  per  cent,  is  made  for  the 
hydrolytic  action  of  the  acid  on  the  dextrin  present. 


22 


other  optically-active  substances  present  have  no  influence 
on  the  result.  (E)  As  the  concentration  of  the  solution 
after  polarizing  ‘ ‘directly”  has  to  be  changed  by  the  addition 
of  the  inverting  acid,  the  “invert  reading”  must  be  corrected 
accordingly. 


CLERQET’S  HETHOD  OF  DOUBLE  POLARIZATION.* 


Prepare  solution  and  polarize  in  the  usual  way.  Take 
50cc  of  the  filtrate  prepared  for  polarizing  and  measured 
out  in  a 50-55cc  double  graduated  flask.  Fill  to  55  mark 
with  hydrochloric  acid,  Sp.  Gr.  1.20.  Heat  gradually  to 
68°C,  taking  about  ten  minutes  to  reach  this  temperature 
(not  less  than  ten  nor  more  than  fifteen.)  [Heat  to  blood- 
heat  (about  40° C)  in  naked  flame,  then  place  in  oven  pro- 
vided for  the  purpose.  Oven  temperature  should  be  about 
120°C.]  Take  temperature  readings  on  a thermometer 
whose  bulb  is  at  the  centre  of  the  bulb  of  the  flask.  When 
at  68°,  cool  at  once  under  running  water.  Wait  till  solu- 
tion has  reached  room  temperature  and  any  lead  precipitate 
has  subsided,  then  polarize  in  a 220  tube  provided  with  a 
thermometer.  Take  temperature  of  the  solution  at  time  of 
polarizing,  to  0.1°C. 

_ (direct  reading)  — (invert  reading) 


144  — 


t 

2 


where  (^)  is  the  temperature  of  the  invert-solution.  If  the 
normal-weight  of  the  original  sample  is  not  used,  multiply 
JV 

by  — . If  200  mm  tube  is  used  for  polarizing  the  invert- 
solution,  multiply  by  ^ . 


DETERHINATION  OF  SPECIFIC=ROTATORY  POWER. 

The  specific-rotatory  powers  of  many  optically  active  sub- 
stances are  not  strictly  constant  when  calculated  from  solu- 
tions of  different  concentration.  While  water  solutions  of 
many  compounds,  as  cane-sugar,  give  values  nearly  iden- 

*This  is  practically  the  original  method  of  Clerget,  which  is  considered  by 
the  author  preferable  to  the  official  German  modification  with  which  it  must 
not  be  confounded.  The  factor  of  calculation  of  the  latter  is  somewhat 
different. 


tical  when  obtained  from  the  different  concentrations  of 
ordinary  laboratory  practice,  there  are  bodies,  as  “invert- 
sugar”  (and  its  characteristic  component,  kevulose),  or 
tartaric  acid,  showing  wide  variation.  Changes  in  temper- 
ature also  often  affect  the  results,  particularly  in  the  case  of 
“ invert-sugar”  and  hevulose. 

For  practical  purposes  of  genQral  work  [re]D  is  calculated 
from  solutions  at  20°C  containing  lOg  of  substance  in  lOOcc, 
its  value  being  taken  as  a constant.  Solutions  from  which 
calculations  of  specitic-rotatory  values  are  to  be  made  are 
prepared  as  nearly  as  possible  at  this  concentration. 

The  true  ( 4 4 absolute  ” ) specific-rotatory  power  at  any 
standard  temperature  is  that  when  the  substance  is  at  the 
concentration  C — 1,  independent  of  the  influence  of  solvents 
on  the  rotation,  a condition  for  polarizing  solids  reached  in 
theory  only,  in  most  cases.  The  influence  of  solvents  can 
be  eliminated  and  this  absolute  value  calculated  with  great 
exactness  by  plotting  the  values  of  the  apparent  specific- 
rotatory  powers  calculated  at  different  concentrations,  using 
abscissae  representing  percentages  of  the  active  substances. 
The  plot  thus  obtained  determines  the  curve  of  influence 
caused  by  the  solvent.  By  analytic  geometry  the  curve  can 
be  extended  till  it  cuts  the  ordinate  at  the  1.00  point.  The 
value  of  this  ordinate  will  be  the  absolute  specific-rotatory 
power  free  from  the  influence  of  solvents.  The  accuracy  of 
this  method  has  been  proved  in  cases  where  specific-rotatory 
values  can  be  determined  when  free  from  or  under  the  influ- 
ence of  different  solvents,  spirits  of  turpentine  being  a case 
in  point. 

Birotation . — Many  substances  when  freshly  dissolved 
give  temporary  readings  which  usually  are  some  simple 
multiple  or  fraction  of  the  constant  reading.  This  tempo- 
rary reading  varies  gradually,  approaching  in  value  the  true 
constant  reading,  which  is  reached  in  a few  hours.  This 
phenomenon  is  known  as  “birotation,”  and  is  supposed  to 
be  caused  by  a gradual  hydration  of  the  dissolved  substance. 
It  can  be  prevented  by  bringing  the  solution  up  to  a boil,  or 
adding  a very  small  quantity  of  ammonium  hydrate.  The 
name  4 4 birotation  ” came  from  the  study  of  dextrose  anhy- 


24 


dride,  which  when  freshly  dissolved  has  a specific-rotatory 
power  for  the  D ray  of  105,  which  gradually  decreases  till 
the  constant  value,  52.8,  is  reached.  It  was  for  a long  time 
supposed  that  this  birotation  was  peculiar  to  dextrose 
anhydride. 

The  Specific  Rotatory  Power  of  Commercial  “Glucose.” 
Commercial  “Glucose”  is  a practically  colorless,  viscid 
syrup  resulting  from  the  hydrolyzing  action  of  acid  at  a 
high  temperature  on  starch-paste.  It  can  be  resolved  into 
three  primary  carbohydrates,  the  proportion  of  each  varying 
in  different  samples  with  the  conditions  of  hydrolysis.  As 
each  of  these  component  carbohydrates  is  optically-active  in 
a different  degree,  the  specific-rotatory  power  of  a sample 
of  commercial  glucose  becomes  a valuable  means  of  deter- 
mining its  quality.  As  all  samples  are  highly  concentrated 
aqueous  solutions  (75-85%)  a determination  of  the  anhy- 
drous substance  is  necessary.  Direct  drying  is  tedious  and 
inaccurate,  and,  as  the  influence  of  a given  concentration  of 
glucose  solution  on  its  specific-gravity  has  not  been  known 
exactly  till  lately,  it  has  become  customary  to  determine  an 
arbitrary  specific-rotatory  power  based  on  an  assumed 
weight  of  anhydrous  substance,  calculated  by  using  the 
specific  gravity  factors  of  cane-sugar.  Thus  the  per  cent  of 
anhydrous  glucose  is  taken  as  the  reading  of  the  Brix  (Bal- 
ling) spindle,  which  in  reality  only  shows  true  percentage  in 
cane-sugar  solutions.  If  these  readings  are  made  on  solu- 
tions of  practically  one  concentration,  taken  as  10%,  the 
error  introduced  is  practically  constant.  The  specific- 
rotatory  powers  thus  obtained  are  proportional  to  the 
absolute  values  by  a constant  factor,  and  hence  strictly 
comparable  with  each  other  in  the  same  proportion  and 
readily  convertible  into  the  latter.  The  influence  of  one 
gram  of  cane-sugar  dissolved  in  100  cubic-centimeters  of 
solution  is  expreseed  by  the  factor,  .00386.  Hence  the 
weight  of  cane-sugar  dissolved  in  100  cubic-centimeters  of 


solution  is  w — 


d — 1 
.00386* 


On  this  account  specific-rotatory 


powers  figured  on  cane-sugar  factors  are  written  [«]D386 
to  distinqnish  them  from  absolute  values.  (Note  that  this 


25 


calculation  gives  grams  in  100  cubic-centimeters , the  Brix 
giving  grams  in  100  grams .) 

[a]D386  °f  Commercial  Glucose. — Method.  Dissolve  about 
50g  [estimate  without  weighing]  in  eight  or  ten  times  its 
bulk  of  water.  Filter  through  two  or  more  thicknesses  of 
paper  to  remove  any  cloudiness.  (Lead  solution  cannot  be 
used  for  clarifying,  as  it  precipitates  dextrin ) . Determine 
Brix  reading  of  solutions  which  should  be  about  10% 
(8-12%.)  Fill  two-decimeter  tube,  and  take  reading  in  a 
quartz-wedge  saccharimeter,  calculating  (a)  by  use  of  the 
factor  obtained  in  determining  the  value  of  one  division  of 
the  saccharimeter  in  angular  degrees  of  yellow  light  rota- 
tion measured  by  glucose. 

Brix- Readings.  Brix  spindles,  like  all  correctly  made 
hydrometers,  should  be  read  along  a line  lying  in  the  plane 
of  the  surface  of  the  liquid  and  not  at  line  of  contact  of  the 
liquid  with  the  stem.  All  readings  not  made  at  the  temper- 
ature at  which  the  instrument  was  graduated,  obviously, 
must  be  calculated  to  this  temperature.  Use  table  of 
temperature  corrections.  The  original  Brix  spindles  were 
made  for  a temperature  of  17.5°C.  Those  used  in  present 
commercial  work  are  more  often  made  for  15°C  or  60°Fh. 

Error  due  to  dissolved  mineral  matter.  — In  a refined  glu- 
cose, such  as  used  in  commerce,  the  organic  matter  other 
than  carbohydrate  is  so  small  as  to  be  negligible.  The 
soluble  mineral  substances  is  often  sufficient  to  affect  the 
density  of  the  solution  to  the  third  decimal  place.  Hence  in 
accurate  work  allowance  must  be  made  for  this  source  of 
error.  This  is  done  by  determining  the  ash  of  the  glucose, 
calculating  the  amount  in  100  cc  of  the  solution  whose  density 
is  to  be  determined,  and  multiplying  this  value  by  .008? 
which  closely  represents  the  influence  on  the  density  of  one 
gram  of  the  mineral  salts  present  in  lOOcc  of  solution.  The 
density  obtained  after  subtracting  this  correction  represents 
that  caused  by  solution  of  the  carbohydrates  alone. 

Determination  of  Ash  of  Commercial  Glucose.  — Take 
lOcc  of  solution  of  known  density.  Evaporate  (practically) 
to  dryness  in  a platinum  dish.  Add  a small  lump  of  vase- 


26 


line  (a  very  small  lump.)  Incinerate  by  placing  dish  in  a 
larger  dish  of  platinum  or  nickel.  This  prevents  over- 
heating and  subsequent  loss  of  chlorides.  Protect  from 
draughts,  and  heat  very  gradually  at  first.  Before  placing 
dish  containing  ash  in  a dessicator,  cover  with  a watch-glass. 


CALIBRATION  OF  SACCHARIMETER  SCALE  BY  THE 
CONTROL=TUBE. 

The  correctness  of  the  saccharimetric  scale  can  be  estab- 
lished at  a few  points  by  comparisons  with  standard  quartz- 
plates  giving  readings  at  these  points.  If  the  surfaces  of  the 
quartz-wedges  are  not  perfect  planes,  it  is  clear  that  such 
comparisons  do  not  suffice  to  standardize  the  instrument,  as 
they  do  not  provide  for  the  possibility  of  slight  irregularities 
of  surface.  It  will  be  noted  that  an  irregularity  no  greater 
than  .0016  of  a millimeter  is  sufficient  to  cause  an  error  of 
0.1%.  By  means  of  the  “control-tube  ” comparisons  can 
be  made  at  any  point  of  the  scale,  using  a solution  of  pure 
cane-sugar  at  three  or  four  concentrations.  The  control- 
tube  is  capable  of  variations  in  length  through  a range  of 
about  100  millimeters,*  its  length  at  any  position  being 
measured  by  a scale  reading  to  0.1  millimeter. 

Since  the  reading  (R)  of  the  saccharimeter  gives  the  per 

cent  of  sugar  in  the  sample  when  w'  — l — 2,  and 

v — 100,  the  equation  for  the  per  cent  of  sugar  at  any 

2 

length  of  tube  under  these  conditions  is  % — . i?p  and  for 


the  reading,  therefore,  R 


°2' 


If  the  normal  weight  of 


chemically-pure  sugar  is  used,  R — — — . 

By  this  means  the  actual  reading  of  the  scale  at  any 
given  length  of  the  control-tube  can  be  compared  with 
the  reading  calculated  for  that  length.  In  exact  work  it  is 
customary  to  make  up  solutions  of  chemically-pure  cane- 


*A  form  of  control-tube  is  made  with  an  inner  cover-glass  so  that  l can  be 
reduced  to  short  lengths,  even  down  to  0.  The  error  introduced  in  determin- 
ing these  very  short  lengths  is  obviously  so  increased  as  to  make  this  modifi- 
cation undesirable. 


27 


sugar  which  can  be  prepared  by  washing  the  finely  pulverized 
granulated  sugar  with  two  or  three  times  its  bulk  of  85% 
alcohol,  drying  at  105°  C,  pulverizing,  and  repeating  the 
whole  process.  Sugar  thus  treated  gives  a reading  of  100 
when  polarized.  [In  this  laboratory,  where  the  exercise 
with  the  control-tube  is  for  practice  in  manipulation,  two 
solutions  of  ordinary  granulated  sugar  are  made  up,  one 
20g  in  lOOcc,  the  other  lOg  in  lOOcc.  Readings  are  taken 
of  each  solution  at  six  different  tube-lengths,  the  per  cent  of 
'sugar  in  the  granulated  sample  being  first  determined  by 
calculation  from  the  six  readings  on  the  20g  solution.  This 
gives  a value  which,  while  it  averages  the  errors  of  these  six 
points,  is  a result  exact  enough  for  the  purpose,  since  the 
average  error  of  a first-class  saccharimeter  is  exceedingly 
small.  Calculate  the  readings  at  each  tube  length,  using  the 

JSFl 

percentage  of  sugar  calculated,  (R  = — -%).  Make  a 

comparison  table  on  bach  of  printed  blank  with  columns 
arranged  as  follows : 

% | w'  | l.  | R (actual)  | R (calculated)  | Dif., 

filling  in  printed  blank  with  other  data  as  usual.] 

Manipulation  of  Control-Tube . — Insert  funnel-plug  and 
fill  tube  just  as  if  of  ordinary  type.  Remove  plug  and 
shorten  tube  by  moving  the  pinion  very  slightly.  This  will 
make  the  solution  fill  up  the  plug-hole.  Insert  funnel  and 
fill  about  half  full  of  solution,  taking  care  not  to  let  air  into 
the  main  tube . It  is  advisable  to  pour  a few  drops  of  sugar- 
solution  through  the  funnel  before  placing  the  latter  in  the 
tube,  as  this  insures  displacement  of  air  in  the  neck  which 
may  otherwise  be  forced  into  the  tube.  The  pinion  should 
work  stiffly  enough  to  avoid  changing  the  length  of  the 
control-tube  in  handling.  Owing  to  the  absorption  of  the 
packing  of  the  telescope  joint,  the  control-tube  must  be 
much  more  thoroughly  rinsed  with  the  solution  than  an 
ordinary  tube,  especially  in  changing  solutions.  Obviously, 
too,  the  tube  should  be  very  thoroughly  washed  and  dried 
after  using.  The  vented  cap  should  be  used  on  the  funnel 
to  avoid  evaporation. 


28 


QUOTIENT  OF  PURITY  (“COEFFICIENT”— “EXPONENT.”) 


This  is 


per  cent  sugar 


: theoretically,  the  per  cent  of  sugar 


per  cent  solids 

in  the  anhydrous  substance.  In  commercial  work,  the  Brix 
reading  is  taken  as  the  per  cent  of  total  solids,  on  the 
assumption  that  the  specific-gravity  of  the  impurities  of 
cane-sugar  solutions  of  commerce  is  the  same  as  that  of  an 
equivalent  amount  of  cane-sugar.  The  error  is  not  a great 
one  in  most  cases  of  cane-sugar  work.  Cane-juices  are 
determined  directly  after  standing  a short  time  to  allow 
escape  of  air.  Syrups,  molasses,  massecuites,  etc.,  are 
diluted  to  about  10°,  Brix. 

While  this  determination,  based  on  an  assumed  factor, 
does  not  give  absolute  results,  it  is  a rapid  means  of  valu- 
ation of  sugar  liquors  on  a constant  basis  of  comparison 
independent  of  concentration.  It  is  of  great  service  in 
measuring  the  efficiency  of  much  work  of  the  sugar-house 
and  refinery. 

General  Directions . Make  up  sample  into  a solution  of 
a density  corresponding  to  10-15%  Brix.  Make  a Brix 
determination.  Find  corresponding  density  in  the  table. 
Fill  a 50-55cc  flask  to  50  mark ; add  2-5cc  of  lead  solution, 
gauging  the  amonnt  according  to  the  impurity  of  the  sample. 
Fill  up  flask  with  water  to  55  mark.  Filter  and  polarize  in 
the  ordinary  manner.  (1)  Density  ( d ) of  the  solution; 
(2)  Reading  (B)  of  the  saccharimeter ; (3)  Its  normal- 
weight  (W)  ; (4)  the  allowance  for  change  in  volume  caused 
by  introduction  of  the  clarifying  agent : are  the  only  data 
necessary  for  determining  the  per  cent  of  sugar  in  the 
solution  as  originally  made  up,  and  hence  by  use  of  the 
Brix  determination  (B)  the  quotient  of  purity  ( Q)  can  be 
calculated.  [Give  a formula  in  terms  of  B,  d,  W and  B for 
Quotient  of  Purity  ($)].  This  method  is  used  in  commer- 
cial work,  as  it  obviates  the  inconvenience  of  weighing  the 
solution  on  a balance,  as  well  as  the  error  introduced  by  the 
low  saccharimeter  readings  of  the  normal  weight  of  so  dilute 
a solution.  A table  calculated  from  the  formula  desired  has 
been  worked  out  by  Schmitz,  by  which  the  per  cent  of  sugar 
can  be  determined  by  inspection  when  the  polarization  and 


29 


Brix  readings  are  made  in  the  manner  described.  This 
table  has  been  corrected  for  the  change  in  specific-rotatory 
power  of  cane-sugar  at  low  concentrations.  In  very  dilute 
solutions  this  affects  the  third  significant  figure. 

REFERENCES. 

General  Chemistry  of  the  Carbohydrates. 

Tollens.  Handbuch  der  Kohlenhydrate.  Vol.  I,  1888.  Vol. 
II : (supplementary)  1895.  (Contains  complete  bibliography  of 
original  papers  prior  to  1895). 

Von  Lippmann.  Chemie  der  Zuckerarten.  1895  (omits  poly- 
saccharids).  (bibliography  of  sugar). 

Technology  of  Sucrose. 

Lock  and  Newlands  Bros.  Handbook  for  Planters  and  Sugar- 
Manufacturers,  1888. 

Horsin-Deon.  Fabrication  de  Sucre.  1882  (also  contains 
analytical  methods). 

Basset.  Guide  pratique  du  Fabricant  de  Sucre.  1882. 

Stohman.  Zuckerfabrikation,  1878. 

Sadtler.  Handbook  of  Industrial  Organic  Chemistry.  1885 
(also  analytical  methods). 

Periodicals.  Cane-sugar  Industry. 

Zeitscrift  der  Vereins  fur  der  Rubenzucker-industrie. 

Neue  Zeitschrift  fur  der  Rubenzucker-industrie. 

Stammer.  Jahrsbericht  tiber  der  Untersuchungen  (etc.)  der. 
Zuckerindustrie. 

The  Sugar-Beet.  Philadelphia. 

Louisiana  Sugar  Planter.  New  Orleans. 

Analytical  Methods  and  Chemical  Control  of  Sugar  Industries. 
Spencer.  Handbook  for  Sugar  Manufacturers,  1889. 

Spencer.  Handbook  for  Beet-Sugar  Manufacturers,  1897. 
Tucker.  Manual  of  Sugar- Analysis,  1890. 

Wiechmann.  Sugar  Analysis,  1890. 

Wiley.  Agricultural  Chemical  Analysis,  Vol.  Ill,  1896. 
Sidersky.  Traite  d’Analyse  der  Matures  Sucries,  1890. 
Fruhling  and  Schultz.  Untersuchungen  der  Rohmaterialen 
(etc.)  der  Zuckerindustrie,  1897. 

Steydn.  Die  Untersuchungen  der  Zuckers  und  der  Zucker- 
haltigen  Stoffen,  1893. 

Lactose. — Analytical  Methods. 

Wiley.  Agric.  Chem.  Analysis,  Vol.  III.  1896. 


30 


Commercial  Glucose : Analytical  and  Technical. 

Heron.  Thorpe’s  Diet,  of  Applied  Chemistry,  (article,. 
“ Sugar.”) 

Report  on  Glucose.  Nat.  Acad,  of  Sciences.  1884  (Analytical 
methods  unreliable). 

Sadtler.  Handbook  of  Indus.  Organic  Chem. 

Allen.  Commercial  Organic  Analysis,  Yol.  1,  1898. 

Spon.  Encyclopaedia  of  Arts  and  Manufactures,  (article,- 
“ Starch.”) 

Sugar  Analysis  Applied  to  Brewing. 

Moritz  and  Morris.  Textbook  of  the  Science  of  Brewing,  1890. 
Optics  of  the  Polariscope  and  General  Theoretical  Principles. 
Landolt.  Handbook  of  the  Polariscope  (translation)  1882. 
Landolt.  Das  optische  Drehungsvermbgen,  1898. 

Tyndall.  Notes  on  Light,  1882. 

Heron.  Thorpe’s  Diet,  of  App.  Chem.  (article:  “Sugar”:; 
section  on  “ Saccharimetry  ”)  (excellent  exposition  of  whole 
subject) . 

TABLES. 

Table  A. 

Brix  and  Specific-Gravity  (8  to  15°  Brix). 


Brix 

Sp.  Gr. 

Brix 

Sp.  Gr. 

8.0 

1.03187 

10.0 

1.04014 

1 

3228 

1 

4055 

2 

3270 

2 

4097 

3 

3311 

3 

4139 

4 

3352 

4 

4180 

5 

3393 

5 

4222 

6 

3434 

6 

4264 

7 

3475 

7 

4306 

8 

3517 

8 

4348 

9 

3558 

9 

4390 

9.0 

1.03599 

11.0 

1.04431 

1 

3640 

1 

4473 

2 

3682 

2 

4515 

S 

3723 

3 

4557 

4 

3765 

4 

4599 

5 

3806 

5 

4641 

6 

3848 

6 

4683 

7 

3889 

7 

4726 

8 

3931 

8 

4768 

9 

3972 

9 

4810 

31 


Brix 

Sq.  Gr. 

Brix 

Sq.  Gr. 

12.0 

1.04852 

14.0 

1.05703 

1 

4894 

1 

5746 

2 

4937 

2 

5789 

3 

4979 

3 

5831 

4 

5021 

4 

5874 

5 

5064 

5 

5917 

6 

5106 

6 

5960 

7 

5149 

7 

6003 

8 

5191 

8 

6047 

9 

5233 

9 

6090 

13.0 

1.05276 

15.0 

1.06133 

1 

5318 

2 

5361 

3 

5404 

4 

5446 

5 

5489 

6 

5532 

7 

5574 

8 

5617 

9 

5660 

Table  B. 


Temperature  Corrections  for  Brix  Readings. 


Degrees  C 
varying  from 

Corrections  in  DegreesT 
Brix  for 

Standard. 

10° 

15° 

Concentrations. 

20° 

7 

.28 

.31 

.34 

1 6 

.24 

.26 

.29 

1 5 

.21 

.23 

.24 

J- 

xn  ^ 

.18 

.19 

.20 

* 3 

.14 

.16 

.16 

1 2 

.10 

.12 

.12 

« ! 

.06 

.06 

.07 

1 

.06 

.06 

.06 

. 2 

.12 

.13 

.13 

1 3 

.19 

.21 

.21 

*§  4 

.26 

.28 

.28 

1 5 

.32 

.34 

.35 

® 6 

.38 

.40 

.41 

5 7 

.44 

.46 

.48 

^ 8 

.51 

.53 

.55 

9 

.58 

.60 

.62 

10 

.65 

.68 

.69 

32 


Table  C. 

Density  of  Water. 


t 

d 

t 

d 

10 

.99974 

20 

.99827 

11 

965 

21 

806 

12 

957 

22 

785 

13 

943 

23 

762 

14 

930 

24 

739 

15 

.99915 

25 

.99714 

15.5 

(.99907) 

26 

681 

16 

900 

27 

654 

17 

884 

28 

626 

17.5 

(.99875) 

29 

597 

18 

866 

30 

.99567 

19 

847 

SPECIFIC=ROTATORY  POWER  OF  QUARTZ. 

As  determined  by  Laurent  Polariscope  (sodium  flame 
passing  through  potash-bichromate)  for  a section  1 mm  thick 
at  20°  : [«]D  = 21.68°  [1  + .000179  (t  — 20)  ].  As  deter- 
mined for  more  strictly  monochromatic  yellow  light  (D  ray 
of  spectrum) , by  passage  of  light  of  sodium  flame  through 
Lippich  “ ray-filter”  (potash-bichromate  and  uranium  sulph- 
ate) for  a section  1 mm  thick  at  20°,  [a]D  = 21.72°. 

CLARIFYING  SOLUTIONS. 

Basic  Lead  Acetate.  — Boil  for  half  an  hour  440  grams  of 
lead  acetate  with  264  grams  of  litharge  in  1500  cc  of  water. 
Cool,  and  dilute  to  two  litres.  Allow  to  subside,  and  siphon 
off  clear  liquor.  (Sp.  gr.  about  1.27,  containing  about  35% 
of  the  basic  salt.) 

Alumina-Cream  Mixture.  — Make  a saturated  solution  of 
potash-alum.  Divide  into  two  parts.  Neutralize  one  part 
with  strongest  ammonic  hydrate.  Add  balance  of  potash- 
alum  solution.  For  decolorizing  dark  solutions,  and  remov- 
ing excess  of  lead. 

SALT=PASTE  FOR  SODIUIT=FLAME  LAiTP. 

(Modified  from  recipe  of  Dupont.) 

Ordinary  effloresced  sodium  hydrogen  phosphate,  three 
parts.  Table  salt,  two  parts.  Sodium  carbonate,  one  part. 
Pulverize,  and  mix  intimately.  Make  into  a stiff  paste  with 
glycerine. 


